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  • Random List of millions of elements in Python Efficiently

    - by eWizardII
    Hello, I have read this answer potentially as the best way to randomize a list of strings in Python. I'm just wondering then if that's the most efficient way to do it because I have a list of about 30 million elements via the following code: import json from sets import Set from random import shuffle a = [] for i in range(0,193): json_data = open("C:/Twitter/user/user_" + str(i) + ".json") data = json.load(json_data) for j in range(0,len(data)): a.append(data[j]['su']) new = list(Set(a)) print "Cleaned length is: " + str(len(new)) ## Take Cleaned List and Randomize it for Analysis shuffle(new) If there is a more efficient way to do it, I'd greatly appreciate any advice on how to do it. Thanks,

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  • I'm new to C++. Please Help me with the Linked List (What functions to add)?

    - by Igal
    DEAR All; Hi, I'm just beginner to C++; Please help me to understand: What functions should be in the Linked list class ? I think there should be overloaded operators << and ; Please help me to improve the code (style, errors, etc,) Thanks for advance. Igal. Please review the small code for the integer List (enclosed MyNODE.h and ListDriver1.cpp); MyNODE.h // This is my first attempt to write linked list. Igal Spector, June 2010. #include <iostream.h> #include <assert.h> //Forward Declaration of the classes: class ListNode; class TheLinkedlist; // Definition of the node (WITH IMPLEMENTATION !!!, without test drive): class ListNode{ friend class TheLinkedlist; public: // constructor: ListNode(const int& value, ListNode *next= 0); // note: no destructor, as this handled by TheLinkedList class. // accessor: return data in the node. // int Show() const {return theData;} private: int theData; //the Data ListNode* theNext; //points to the next node in the list. }; //Implementations: //constructor: inline ListNode::ListNode(const int &value,ListNode *next) :theData(value),theNext(next){} //end of ListNode class, now for the LL class: class TheLinkedlist { public: //constructors: TheLinkedlist(); virtual ~TheLinkedlist(); // Accessors: void InsertAtFront(const &); void AppendAtBack(const &); // void InOrderInsert(const &); bool IsEmpty()const;//predicate function void Print() const; private: ListNode * Head; //pointer to first node ListNode * Tail; //pointer to last node. }; //Implementation: //Default constructor inline TheLinkedlist::TheLinkedlist():Head(0),Tail(0) {} //Destructor inline TheLinkedlist::~TheLinkedlist(){ if(!IsEmpty()){ //list is not empty cout<<"\n\tDestroying Nodes"<<endl; ListNode *currentPointer=Head, *tempPtr; while(currentPointer != 0){ //Delete remaining Nodes. tempPtr=currentPointer; cout<<"The node: "<<tempPtr->theData <<" is Destroyed."<<endl<<endl; currentPointer=currentPointer->theNext; delete tempPtr; } Head=Tail = 0; //don't forget this, as it may be checked one day. } } //Insert the Node to the beginning of the list: void TheLinkedlist::InsertAtFront(const int& value){ ListNode *newPtr = new ListNode(value,Head); assert(newPtr!=0); if(IsEmpty()) //list is empty Head = Tail = newPtr; else { //list is NOT empty newPtr->theNext = Head; Head = newPtr; } } //Insert the Node to the beginning of the list: void TheLinkedlist::AppendAtBack(const int& value){ ListNode *newPtr = new ListNode(value, NULL); assert(newPtr!=0); if(IsEmpty()) //list is empty Head = Tail = newPtr; else { //list is NOT empty Tail->theNext = newPtr; Tail = newPtr; } } //is the list empty? inline bool TheLinkedlist::IsEmpty() const { return (Head == 0); } // Display the contents of the list void TheLinkedlist::Print()const{ if ( IsEmpty() ){ cout << "\n\t The list is empty!!"<<endl; return; } ListNode *tempPTR = Head; cout<<"\n\t The List is: "; while ( tempPTR != 0 ){ cout<< tempPTR->theData <<" "; tempPTR = tempPTR->theNext; } cout<<endl<<endl; } ////////////////////////////////////// The test Driver: //Driver test for integer Linked List. #include <iostream.h> #include "MyNODE.h" // main Driver int main(){ cout<< "\n\t This is the test for integer LinkedList."<<endl; const int arraySize=11, ARRAY[arraySize]={44,77,88,99,11,2,22,204,50,58,12}; cout << "\n\tThe array is: "; //print the numbers. for (int i=0;i<arraySize; i++) cout<<ARRAY[i]<<", "; TheLinkedlist list; //declare the list for(int index=0;index<arraySize;index++) list.AppendAtBack( ARRAY[index] );//create the list cout<<endl<<endl; list.Print(); //print the list return 0; //end of the program. }

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  • How to use Delegate in C# for Dictionary<int, List<string>>

    - by Emanuel
    The code: private delegate void ThreadStatusCallback(ReceiveMessageAction action, Dictionary<int, List<string>> message); ... Dictionary<int, List<string>> messagesForNotification = new Dictionary<int, List<string>>(); ... Invoke(new ThreadStatusCallback(ReceivesMessagesStatus), ReceiveMessageAction.Notification , messagesForNotification ); ... private void ReceivesMessagesStatus(ReceiveMessageAction action, object value) { ... } How can I send the two variable of type ReceiveMessageAction respectively Dictionary<int, List<string>> to the ReceivesMessagesStatus method. Thanks.

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  • List and ReadOnly property

    - by Luca
    List (and List) instances can be readonly, seeing ReadOnly property; methods throws exceptions in the case the collection have the property ReadOnly property. How can I create readonly List instances? What are the main uses?

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  • list comprehension example

    - by self
    can we use elif in list comprehension? example : l = [1, 2, 3, 4, 5] for values in l: if values==1: print 'yes' elif values==2: print 'no' else: print 'idle' can we use list comprehension for such 2 if conditions and one else condition? foe example answer like : ['yes', 'no', 'idle', 'idle', 'idle'] I have done till now only if else in list comprehension.

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  • Downsampling the number of entries in a list (without interpolation)

    - by Dave
    I have a Python list with a number of entries, which I need to downsample using either: A maximum number of rows. For example, limiting a list of 1234 entries to 1000. A proportion of the original rows. For example, making the list 1/3 its original length. (I need to be able to do both ways, but only one is used at a time). I believe that for the maximum number of rows I can just calculate the proportion needed and pass that to the proportional downsizer: def downsample_to_max(self, rows, max_rows): return downsample_to_proportion(rows, max_rows / float(len(rows))) ...so I really only need one downsampling function. Any hints, please? EDIT The list contains objects, not numeric values so I do not need to interpolate. Dropping objects is fine.

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  • How to re-order a List<String>

    - by tarka
    I have created the following method: public List<String> listAll() { List worldCountriesByLocal = new ArrayList(); for (Locale locale : Locale.getAvailableLocales()) { final String isoCountry = locale.getDisplayCountry(); if (isoCountry.length() > 0) { worldCountriesByLocal.add(isoCountry); Collections.sort(worldCountriesByLocal); } } return worldCountriesByLocal; } Its pretty simple and it returns a list of world countries in the users locale. I then sort it to get it alphabetic. This all works perfectly (except I seem to occasionally get duplicates of countries!). Anyway, what I need is to place the US, and UK at the top of the list regardless. The problem I have is that I can't isolate the index or the string that will be returned for the US and UK because that is specific to the locale! Any ideas would be really appreciated.

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  • Multithreaded linked list traversal

    - by Rob Bryce
    Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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  • Can I Cast a Generic List by Type??

    - by CrazyJoe
    NavigatorItem NavItem = (NavigatorItem)cboItems.SelectedItem; lblTitle.Text = NavItem.Title; RadWrapPanel Panel = new RadWrapPanel(); Type t = NavItem.ItemsType; //<------ The Type inside my List is here. List<???> items = (List<???>)NavItem.Items; // <----Here Is the problem foreach (object item in items) { Panel.Children.Add((UIElement)Activator.CreateInstance(NavItem.Display,item)); } ItemsContainer.Content = Panel; In code above i need to get the type of items on t variable to put into of my generic List. Help Please!!!

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  • Checkbox Images in List

    - by Bridget
    It seems like it should be a simple concept. I need a vertical list. This list has an image with a checkbox and pathname of that image underneath it. The user should be able to check the checkboxes of the images they want to appear in their "shopping cart". The images, checkbox label, and list are populated by an XmlList. How can I do this in Flex 3.5 and Actionscript and have a button that when clicked, display a list of the checked items??

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  • PHP/Codeigniter processing a list with javascript

    - by user270797
    I have a list of items that the user can select. I want it to be more user friendly than standard checkboxes so I have seperate div's each with a unique id. When user clicks an item, I use javascript to display a tick on top of that item and change the style to show that it is highlighted. Im trying to work out how I can pass the list of id's when the form is submitted. Remember, if the user unticks an item, it should be removed from the list, I was thinking of using comma seperated values in a hidden text field but couldnt work out how to remove items from the start of the list if they were deselected

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  • removing elements incrementally from a list

    - by Javier
    Dear all, I've a list of float numbers and I would like to delete incrementally a set of elements in a given range of indexes, sth. like: for j in range(beginIndex, endIndex+1): print ("remove [%d] => val: %g" % (j, myList[j])) del myList[j] However, since I'm iterating over the same list, the indexes (range) are not valid any more for the new list. Does anybody has some suggestions on how to delete the elements properly? Best wishes

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  • Beginning android: how to map a string to a list

    - by user569421
    I just finished the NotepadV1-3 tutorial for Android apps, and I was thinking of creating my own inventory app for fun, which for now basically consists of a list of names (such as "DVD" or "Grocery"), each of which can be clicked, which will bring up another specific list associated with that name. However, with the SQLiteDatabase.insert(..) method, the ContentValue can only take (among many others) "String, String" as argument, and I can't figure out how to input into the database a list of Strings associated with a particular key. I'm having trouble researching on how to resolve this as I am not that familiar with SQL. What would be the best way to store a key with its associated list of Strings? Any pointers and suggestions are appreciated! Android newb :[

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  • Adding nodes to a global linked-list

    - by Zack
    I am attempting to construct my first linked list, and having read a basic introduction, have done the following. Firstly, declare a linked list node as: struct errorNode { uint8 error; struct errorNode* next; }; Secondly, define the first node globally as: struct errorNode errorList = {0, NULL}; This has been done to allow each of the libraries that make up my current project to insert errors into a common list. The function to do this is: void errorListWrite(uint8 error) { struct errorNode* newNode = malloc(sizeof(struct errorNode)); newNode->error = error; newNode->next = &errorList; errorList = *newNode; } Whilst this compiles without error, it does not function as expected. I thnk the problem is with the last two statements of the list write function, but I am unsure. A hint as to what I am doing wrong would be most appreciated.

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  • Good practice of using list of function in Python

    - by riskio
    I am pretty new to python and I discovered by myself that I can create a list of function and call with a for loop. example: def a(args): print "A" def b(args): print "B" def c(args): print "C " + str(args) functions = [a,b,c] for i in functions: i(1) So, my question is: is there any good practice or elegant way to use list of functions and what is a good use of all this? (do have a particular name the "list of functions"?) thank you

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  • Forbid public Add and Delete for a List<T>

    - by aaginor
    Hi folks, in my C#-project, I have a class which contains a List public class MyClass { public MyClass parent; public List<MyClass> children; ... } I want to prevent the user of the class from Adding (and Deleting) an Element to the children-List, but he shall still be able to parse its elements. I want to handle the Adding and Deleting within MyClass, providing an AddChild(MyClass item) and DeleteChild(MyClass item) to ensure that, when an item is added to the child list, the parent of that item will be set properly. Any idea how to do this besides implementing my own IList? Thanks in advance, Frank

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  • Fill a array with List data

    - by marionmaiden
    How can I fill a array with the data provided by one List? For example, I have a List with Strings: List l = new ArrayList<String>(); l.add("a"); l.add("b"); l.add("c"); then I want to copy this data into a String array: String[] array = ?

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  • django template find value within list

    - by dotty
    Hay, how do i find a value with in python list in django's template system? example list = [1,2,3,4,5,6,7] x = 1 if x is in list: return u'found!' else: return u'not found' endif: Something along those lines. any help would be great

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  • Can't remove first node in linked list

    - by carlmonday
    I'm trying to make a linked list class in python (pointless I know, but it's a learning exercise), and the method I have written to remove a node doesn't work if I try to remove the first element of the linked list. If the node to be removed is anywhere else in the linked list the method works fine. Can someone give me some insight as to where I've gone wrong? Here's my code thus far: class Node: def __init__(self, data=None, next=None): self.data = data self.next = next def __repr__(self): return repr(self.data) def printNodes(self): while self: print self.data self = self.next def removeNode(self, datum): """removes node from linked list""" if self.data == datum: return self.next while self.next: if self.next.data == datum: self.next = self.next.next return self self = self.next

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  • Python - Create a list with initial capacity

    - by Claudiu
    Code like this often happens: l = [] while foo: #baz l.append(bar) #qux This is really slow if you're about to append thousands of elements to your list, as the list will have to constantly be re-initialized to grow. (I understand that lists aren't just wrappers around some array-type-thing, but something more complicated. I think this still applies, though; let me know if not). In Java, you can create an ArrayList with an initial capacity. If you have some idea how big your list will be, this will be a lot more efficient. I understand that code like this can often be re-factored into a list comprehension. If the for/while loop is very complicated, though, this is unfeasible. Is there any equivalent for us python programmers?

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  • concurrent doubly-linked list (1 writer, n-readers)

    - by Arne
    Hi guys, I am back in the field of programming for my Diploma-thesis now and stumbled over the following issue: I need to implement a thread-safe doubly-linked list for one thread writing the list at any position (delete, insert, mutate node data) and one to many threads traversing and reading the list. I am well aware that mutexes can be used to serialize access to the list, still I presume that a naive lock around any write operation will be less than optimal. I am wondering whether there are better variants. (I am well aware that 'optimal' has not much of a practical meaning as long as no exact measure/profiling are available but this is an academic thesis after all..) I am very gratefull for code-samples as well as references to academic granted these have at least a tiny bit of practical relevance. Thanks at lot

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  • Scrolling down an awt.List

    - by nico
    As from subject, I have an awt.List object. When I add something to the list I would like to scroll it down to show the last inserted object. For instance: myList.add("sometext"); myList.select(myList.getItemCount()-1); myList.showSelectedItem(); // Or something like that The documentation does not seem to list any method that does something like that, can anybody help please?

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  • String contains all the elements of a list

    - by CSSS
    I am shifting to Python, and am still relatively new to the pythonic approach. I want to write a function that takes a string and a list and returns true if all the elements in the list occur in the string. This seemed fairly simple. However, I am facing some difficulties with it. The code goes something like this: def myfun(str,list): for a in list: if not a in str: return False return True Example : myfun('tomato',['t','o','m','a']) should return true myfun('potato',['t','o','m','a']) should return false myfun('tomato',['t','o','m']) should return true Also, I was hoping if someone could suggest a possible regex approach here. I am trying out my hands on them too.

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  • Java: set-size List issue UnsupportedOperationException thrown

    - by tuckster
    I am having a problem changing a List that has a set-size in Java. I understand that I can't add or remove from this list but why can't I use set? When I use set the UnsupportedOperationException is thrown as well as when I use add and remove which is expected. set public Object set(int index, Object element) Replaces the element at the specified position in this list with the specified element (optional operation). I understand its an optional operation its just that want to replace that one element of the list with another element. Is there any way I can do this?

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